1. Field of The Invention
The present invention relates generally to a disk cartridge. Particularly, the present invention relates to a type of disk cartridge which may be applied to an optical or a magneto-optical disk etc., which requires fewer production steps and is stable and reliable for information storage and retrieval applications.
2. Description of The Prior Art
In the various information retrieval and storage media technologies, for example, magnetic, magneto-optical and optical disk media, if dust or other material impinges on a recording surface of the media, errors are apt to occur during reading and/or writing of the information on the disk.
For this reason disk information storage and retrieval media (hereinbelow: disk) are usually housed in a protective cartridge casing. Examples of such disk cartridges are disclosed in U.S. Pat. Nos. 4,797,770 and 4,799,121. According to these disclosures, opposing upper and lower halves of a cartridge casing are joined by screws, ultrasonic welding or the like into a cartridge/shutter assembly. In one of the halves of such disk cartridge assemblies, an opening for a rotary driving means is formed in a substantially center portion thereof for chucking the disk on a turntable of a disk drive.
Further, a shutter protects an opening for a read/write head such as an optical head, for example, of a disk drive which accesses the disk for reading data from and/or writing data to at least one side of the disk. The shutter is generally U-shaped in cross-section and slidably disposed to open and close for exposing and cover the disk surface respectively.
The shutter and the disk cartridge receive therein a rotatably mounted disk, the disk substrate may generally be formed of a polycarbonate such as PMMA (polymethyl methacrylate), glass, or other suitable material for example.
In the case of optical disks, a material with suitable optical characteristics is necessary. On the side opposite that of a transparent optical substrate, a reflective read/write layer and a protective layer for protecting the read/write layer are formed. Such optical disk arrangements are disclosed in U.S. Pat. Nos. 4,787,009 and 4,829,510.
In the above mentioned disclosures, a magnetic plate is provided in a central portion of the disk for coupling with a rotational driving means of the disk drive turntable for simplifying alignment of the disk for read and/or write operations. In optical disk cartridges, this magnetic plate is substantially circular and positioned at a center portion of the disk cartridge. The magnetic plate is joined to the disk substrate with adhesive or is retained in a ring of synthetic resin which is joined to the disk by ultrasonic welding or the like.
In disk loading operations the spindle of a disk drive turntable is aligned with a center of the magnetic portion for correctly positioning the disk axially for read and/or write operations.
In these disk cartridges, a center hole of the magnetic plate decides the surface orientation of the disk and decentering of the disk may occur. Further, even if adhesion is accurately carried out the adhesive and the disk material often have different expansion characteristics when exposed to humidity or temperature variations and warping, due to shrinkage or expansion of the adhesive, for example, which may easily cause read and/or write errors to occur.
Therefore, it has been required to provide a disk cartridge in which decentering of the disk may be prevented to avoid damage to the disk and/or the disk drive.